Remove trailing / from export of GOPATH (#1282)

In the docs, there's a / too much when exporting the variables. This
resulted in a double slash in the path, if copy-pasting the commands
straight from docs.

docs/developer/apprepository-controller.md

@@ -17,7 +17,7 @@ The `apprepository-controller` is a Kubernetes controller for managing Helm char
 ## Environment
 
 ```bash
-export GOPATH=~/gopath/
+export GOPATH=~/gopath
 export PATH=$GOPATH/bin:$PATH
 export KUBEAPPS_DIR=$GOPATH/src/github.com/kubeapps/kubeapps
 ```

docs/developer/build.md

@@ -13,7 +13,7 @@ This guide explains how to build Kubeapps.
 ## Environment setup
 
 ```bash
-export GOPATH=~/gopath/
+export GOPATH=~/gopath
 export PATH=$GOPATH/bin:$PATH
 export KUBEAPPS_DIR=$GOPATH/src/github.com/kubeapps/kubeapps
 ```

docs/developer/chart-repo.md

@@ -15,7 +15,7 @@ The `chart-repo` component is tool that scans a Helm chart repository and popula
 ## Environment
 
 ```bash
-export GOPATH=~/gopath/
+export GOPATH=~/gopath
 export PATH=$GOPATH/bin:$PATH
 export MONOCULAR_DIR=$GOPATH
 ```

docs/developer/chartsvc.md

@@ -15,7 +15,7 @@ The `chartsvc` component is a micro-service that creates an API endpoint for acc
 ## Environment
 
 ```bash
-export GOPATH=~/gopath/
+export GOPATH=~/gopath
 export PATH=$GOPATH/bin:$PATH
 export MONOCULAR_DIR=$GOPATH
 ```

docs/developer/dashboard.md

@@ -17,7 +17,7 @@ The dashboard is the main UI component of the Kubeapps project. Written in Javas
 ## Environment
 
 ```bash
-export GOPATH=~/gopath/
+export GOPATH=~/gopath
 export PATH=$GOPATH/bin:$PATH
 export KUBEAPPS_DIR=$GOPATH/src/github.com/kubeapps/kubeapps
 ```

docs/developer/tiller-proxy.md

@@ -14,7 +14,7 @@ The `tiller-proxy` component is a micro-service that creates a API endpoint for
 ## Environment
 
 ```bash
-export GOPATH=~/gopath/
+export GOPATH=~/gopath
 export PATH=$GOPATH/bin:$PATH
 export KUBEAPPS_DIR=$GOPATH/src/github.com/kubeapps/kubeapps
 ```